According to U.S. News and World Report, about 300,000 of the 10 million Americans who hurt their backs each year wind up on the operating table. Most of the operations are for ruptured discs, the rubbery, shock-absorbing cushions between the bones of the spine. Among humans, herniated discs are a common cause of back trouble. According to the National Center for Health Statistics' (NCHS) Health Interview Survey, there are more than two and a half million men and women in the United States with displaced discs, half of them with trouble severe enough that they saw a doctor or had to limit their activities.
Shooting pains down the leg, called sciatica, that persist for six weeks or so probably mean that the gelatinuos material inside the disc, the nucleus pulposus, has leaked through the fibrous outer portion, the annulus fibrosus, forming a hernia which is pressing on a nerve. Though the popular misnomer for this condition is a "slipped disc", there is, in fact, no slippage. Instead, the affected disc balloons out from between the bony parts of the vertebrae. FIGS. 1 and 2 illustrate a normal disc, while FIGS. 2 and 3 show a herniated disc. Herniation most frequently affects the forth and fifth discs in the lumbar region although this problem can also occur in the uppermost vertebrae (cervical) around the neck.
If the ruptured disc presses on a nerve root in such a way to cause muscular weakness or interference with bladder function, most physicians recommend immediate surgery to remove the disc and thus relieve the pressure on the nerve. Such surgery is called a diskectomy (literally, removal of a disc) or sometimes a laminectomy, because surgeons usually cut through the lamina of a vertebra (the portion between the spinous and transverse process) to get at the disc.
In a laminectomy, access to the nucleus is made by cutting a channel from the rear of the patient's back through the vertebral lamina to the disc. Because of this cutting, a laminectomy is a very destructive process, which often leads to permanent scarring with more pain than the original prolapsed disc. Another disadvantage is that laminectomies often require long hospitalization and postoperative recovery periods, typically from one to two months, if there have been no complications.
Back surgery candidates naturally want the least invasive form of disc surgery. A patient with a contained disc herniation (FIGS. 3 and 4) might be referred for discectomy, microdiscectomy, (automated or manual) percutaneous discectomy, arthroscopic discectomy, laser-assisted disc decompression (LDD), or chemonucleolysis. One major disadvantage of all of these less-invasive disc procedures is that they are limited to contained herniations, which are protrusions in which disc material has not broken through the annulus.
Chemonucleolysis was the first of the less invasive surgical techniques used to treat contained disc herniations. In 1982, the Food and Drug Administration approved this drug treatment. The drug, chymopapain, is injected into the central portion, the nucleus pulposus, of the diseased disc to dissolve some of the disc substance in an attempt to relieve pressure against a nerve or other soft tissue.
One major disadvantage associated with the use of chymopapain is that one out of every one hundred people can suffer a severe allergic reaction called anaphylaxis. Occasionally, this allergic reaction is fatal.
A further disadvantage is that if severe or moderate pain persists, with or without nerve root pressure, and chemonucleolysis either failed or was not deemed advisable by a surgeon, an operation will still be necessary.
Another known procedure is a microsurgical diskectomy (microdisectomy), a similar technique to arthroscopic knee surgery. As in laminectomy, the disc is accessed by cutting a channel from the rear of the patient's back to the disc, but the microscope permits the surgeon to operate through a smaller incision--typically 1 to 1.5 inches, compared with about 2.4 inches for conventional discectomy. With the use of an operating microscope, smaller diameter microsurgical instruments can pass through the vertebral laminae without bone cutting. Although microsurgical diskectomy has fewer complications and shorter hospital stay than laminectomy, blood vessels and nerves are still retracted, and scarring and post operative pain is not eliminated.
Another disadvantage of microdiscectomy is that it because of the small incision, surgeons may find themselves exploring the wrong spinal level, missing pathology that is outside of the limited operating field, or damaging neural structures. Additionally, if hemorrhaging is not controlled, the surgeon's view of the operating field can be severely compromised. Infection is another worry, as it is difficult to completely sterilize the operating microscope.
It has been stressed that this type of disc surgery is most effective only in younger individuals who have so-called "soft herniations"--i.e. when the nerve root compression is caused solely by protruding soft tissue, also known as "contained herniations". Noncontained herniations, or sequestered discs, in which disc fragments have migrated beyond the border of the annulus, are not accessible with this approach.
Percutaneous diskectomy is an alternative minimal-surgery procedure developed for treatment of herniated discs. The procedure is done with either manual instruments, such as pituitary rongeurs, or an automated suction aspiration probe called the nucleotome. The procedure consists of placing a long-bore needle through the back muscles on one side of the spine right into the center of the disc. A tiny blade is passed through the needle into the center of the disc, and this cutting blade is used to mince the inner disc tissues. This material is then asperated out of the body by suction through an inner tube within the needle. The result is a creation of a hole within the disc similar to that which occurs when the disc is dissolved by chemonucleolysis. The bulging disc material can then collapse back in toward the center of the disc. This "debulking" of the disc theoretically reduces pressure on the adjacent spinal nerves, relieving symptoms.
An example of manual percutaneous discectomy is illustrated in U.S. Pat. No. 4,545,374 to Jacobson, incorporated herein by reference. Jacobson generally describes a method and instruments for performing a percutaneous lumbar disectomy. In order to remove disc nucleus material, a cannula is passed laterally through the body. Disc removal instruments are then passed through the cannula to the disc. To help the surgeon visually monitor the area around the injured disc and prevent improper positioning of the instruments, fluorscopic X-ray may be used.
One major disadvantage associated with the percutaneous diskectomy procedure, like that described in Jacobson, is that percutaneous discectomy only removes material from the center of the disc. It does not allow the surgeon to excise fragments that had migrated toward the back and sides. Although these fragments sometimes retract when nuclear material is removed from the center, they will often migrate to the periphery of the disc. If left in place, the fragments can cause recurrent radicular symptoms.
Another disadvantage is that noncontained herniations, or sequestered herniations are unsuitable for this technique. The originator of the automated percutaneous discectomy, Gary Onik, M.D. recommends using this procedure in herniations that are localized in front of the intervertebral space and have not broken through the annulus.
Laser-assisted disc decompression (LDD) is another technique to reduce the amount of hydraulic pressure inside of a contained herniated disc. In LDD, the surgeon vaporizes the disc nucleus material to relieve pressure.
An example of this method of surgery is illustrated in U.S. Pat. No. 5,084,043 to Hertzmann et al., incorporated herein by reference. Hertzmann generally describes a method for performing percutaneous diskectomy using a laser to vaporize material in the nucleus pulposus. Conventionally, a computed tomograph (CT) scan slice of the whole abdomen through the involved disc is used to help determine the entry path.
A disadvantage of all of these less-invasive procedures is that when the bulge has actually broken through the annulus fibrosis (noncontained hernia or prolapse), the bulging disc material may be prevented from collapsing back in toward the center of the disc. Thus, removal of disc material from the nucleus pulposus will not remove the bulge which is causing the painful pressure on nerves.
One possible solution to these problems is to provide a less-invasive procedure which actually removes the bulge or prolapse itself for noncontained herniated discs within the spinal foramen.
Another possible solution to these problems is to provide a procedure which does not involve operating on the nonherniated portion of the nucleus pulposus.
Another possible solution to these problems is to provide a procedure which does not involve chemical side effects or allergic reactions.
Another possible solution is to provide a procedure which requires a minimal hospitalization period and post-operative recovery time.
A further solution to these problems is to provide a procedure in which the surgeon can visually monitor the procedure though a specially designed optical system.
Thus, there is a need in the art for a less-invasive procedure which actually removes the bulge or prolapse itself for noncontained herniated discs within the spinal foramen and which does not involve operating on the nonherniated portion of the nucleus pulposus.
There is an additional need in the art for a procedure which does not involve chemical side effects or allergic reactions and requires only a minimal hospitalization period and post-operative recovery time.
There is an additional need in the art for a procedure in which the surgeon can visually monitor the procedure though a specially designed optical system.